Osmotic dosage systems comprising means for delivering a solid drug formulation by displacing physically the solid drug formulation from the osmotic system are known to the prior art in U.S. Pat. Nos. 4,327,725; 4,612,008; 4,765,989; and 4,783,337.
An osmotic system comprising means for displacing physically a liquid drug formulation from an osmotic system is known to the prior art in U.S. Pat. No. 4,627,850. U.S. Pat. No. 3,995,631 describes a dosage form having an impermeable flexible bag containing a liquid drug formulation surrounded by an osmotic layer. U.S. Pat. No. 4,203,440 describes a somewhat similar configuration in which a semipermeable layer in which is dispersed an ion exchange resin forms an osmotic layer surrounding a flexible bag from which drug is dispensed. U.S. Pat. No. 4,627,850 describes a capsule surrounded by an osmotic layer and outer, semi-permeable layer to dispense drug from the capsule upon expansion of the osmotic layer. U.S. Pat. No. 5,324,280, which is incorporated herein by reference, describes a gelatin capsule filled with a liquid drug formulation wherein the capsule is surrounded by an osmotic layer and an outer, semipermeable layer. Upon imbibing fluid that passes through the semipermeable membrane, the osmotic layer expands and forces the liquid drug formulation from an exit passageway formed in the end of the dosage form. While the foregoing system of U.S. Pat. No. 5,324,280 may provide controlled release of the active agent in particular circumstances, its use with gelatin capsules has not been entirely satisfactory for wide application.